The present invention relates to an electric contact element having a succession of layers comprising a base material, a contact layer and a thin galvanically deposited gold-containing surface layer.
Contact elements of this type are used, for example, in the fields of communications technology and data processing. With electric plug-in connections, they are configured, for example, as contact blade and contact clip. They distinguish themselves by the fact that their contact resistance is as low as possible and remains as constant as possible over an extended service life. Contact elements of the type comprising a base material, for example brass, and an overlying contact layer of palladium or palladium-nickel, upon which a surface layer of hard gold or soft gold is galvanically deposited, are being widely used. Contact elements of this type are known, for example, from the paper by E. J. Kudrak et al. published in "Plating and Surface Finishing", February 1992, pp. 49 to 54. The contact elements described by this publication comprise a contact layer of palladium or palladium-nickel of a thickness of between 0.25 and 2.5 .mu.m and galvanically deposited surface layers of hard gold. The gold-containing surface layers, known as "flash", usually have a thickness of less than 0.5 .mu.m.
A contact element of the kind from which this application starts out has been known also from DE-O-S 25 40 944. The contact element of this publication, which is intended for electric plug-in contacts, consists for example of a support comprising an easily soldering and welding intermediate layer, with an overlying contact layer of a silver-palladium alloy containing 30% by weight of palladium, on which a porous gold. layer of a thickness of 0.2 .mu.m is galvanically deposited.
The gold-containing surface layer has proven its value, under aspects of their non-tarnishing properties, optimum maintenance of a constant contact resistance and maximum wear resistance, in connection with contact elements having contact surfaces of different materials, especially of alloys containing palladium. On the other hand, however, the gold-containing surface is a cost factor of considerable weight, especially for applications using a plurality of electric contact surfaces. However, due to the mechanical stresses acting on the contact element, and especially on the surface layers, during making and breaking of the electric contact, a certain minimum thickness is required for the surface layers of the known contact elements. Usually, a minimum thickness of approximately 0.20 .mu.m is observed.